<style>
  .mercury-panel {
    position: absolute;
    height: 100px;
    width: 100px;
  }
  #panel_container {
    position: absolute;
    top: 42px;
    left: 42px;
    width: 20px;
    height: 20px;
  }
</style>
<div id="panel_container"></div>
<div id="button"></div>